Multi-purpose icebreaker

ABSTRACT

The invention is a multi-purpose icebreaker having main propulsion devices in the front part of the vessel and steering device in the aft part of the vessel. This kind of icebreaking vessel has excellent steering characteristics and it can efficiently and constantly push the ice field. The main propulsion devices at the bow are azimuth propulsion devices or conventional shaft propulsion devices. The steering devices are tunnel thrusters or smaller azimuth thrusters.

FIELD OF THE INVENTION

The present invention relates to a multi-purpose icebreaker having a front part, an aft part, main propulsion devices and steering devices.

PRIOR ART

The conventional icebreakers are provided with shaft propellers and rudders at the stern of the vessel. In order to increase power for ice breaking the shaft propellers were added also in the front of the vessel.

In the first multi-purpose icebreakers the shaft propellers and rudders at the stern of the vessel have been substituted by azimuth propellers, which essentially improved the steering characteristics of the ship. Therefore in the front of the vessel it was necessary to provide only with several steering tunnel thrusters.

Many different modifications have been presented for improving icebreaking vessels. The document U.S. Pat. No. 5,218,917 presents a special icebreaking ship, which has azimuth propellers at the stern of the ship. The special feature of this vessel is that only the aft part of the ship is optimized for braking ice and the forward part of the ship is optimized for open water conditions. The purpose of this is that normally in open water the ship is moving forward and in heavy ice conditions the ship is breaking ice by moving in the aft direction.

The document U.S. Pat. No. 5,996,520 presents an icebreaking ship having azimuth propellers at the both ends of the ship. Because of the characteristics of the azimuth propellers the ship is easily capable to move into any direction. The special feature of this vessel is that the hull of the ship is specially designed to move sideward, which means slightly a side against the ice field. The purpose of that is to make into the ice field a passage, which is wider than the breadth of the ship.

An object of the present invention is to provide an improved multi-purpose icebreaker. The second purpose of the invention is to provide a multi-purpose icebreaker, which has improved steering characteristics and which is efficient at continuous slow speed in heavy ice conditions, especially when ice ridges may occur.

SUMMARY OF THE INVENTION

The features of the invention are described in the characterizing part of claim 1. The icebreaker according to the invention is characterized in that in the multi-purpose icebreaker at least one main propulsion device is located in the front part of the vessel and at least one steering device is located in the aft part of the vessel.

The benefit of the arrangement is that this kind of icebreaking vessel has excellent steering characteristics. By using the main azimuth propulsion devices located at the bow of the ship, the vessel can easily turn to any direction. The icebreaking vessel can push the ice field efficiently forward and also to both sides if for example the passage has to be made wider for the ship towed.

The icebreaking ship provided with azimuth propulsion devices at the front part of the ship is especially useful in the situations, where the ship has to move slowly in the in heavy ice conditions, and when ramming is not possible. These characteristics are also useful, when the ship has to stay at a predetermined position in a moving ice field. Such needs occur for example on the oil fields at arctic seas.

According to a preferred embodiment of the invention the multi-purpose icebreaker has in the front part of vessel two main propulsion devices, which are azimuth propulsion devices, and in the aft part of the vessel the steering device comprises one or more tunnel thrusters.

According to a second preferred embodiment of the invention in the multi-purpose icebreaker the main propulsion device in the front part of vessel comprises two azimuth propulsion devices, and that the steering device in the aft part of the vessel comprises one or more azimuth propulsion devices, which are smaller than the main propulsion devices in the front part of the ship.

According to a third preferred embodiment of the invention in the multi-purpose icebreaker the main propulsion device in the front part of the vessel comprises two conventional shaft propulsion devices, and the steering device in the aft part of the vessel comprises one or more azimuth propulsion devices.

According to a fourth preferred embodiment of the invention in the multi-purpose icebreaker the main propulsion device in the front part of the vessel comprises two conventional shaft propulsion devices, and the steering device in the aft part of the vessel comprises one or more tunnel thrusters.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in the following by means of an example, with reference to the appended drawings in which

FIG. 1 presents a side view of an embodiment of the multi-purpose icebreaker according to the invention.

FIG. 2 presents a side view of the second embodiment of the multi-purpose icebreaker according to the invention.

FIG. 3 presents a side view of the third embodiment of the multi-purpose icebreaker according to the invention.

FIG. 4 presents a side view of the multi-purpose icebreaker of FIG. 1 attached to a turret and operating as an offloading icebreaker on an oil field under the sea

FIG. 5 presents a bottom view of an embodiment of the multi-purpose icebreaker according to the invention.

DESCRIPTION OF THE DRAWINGS

FIG. 1 presents a multi-purpose icebreaker 10 being attached to another ship 11. The purpose of the attachment is for example that the icebreaker 10 is towing the other ship 11. However, the attachment may be for other reasons, as described below.

In FIG. 1 the water 12 is described as open water, but of course because the vessel 10 is an icebreaker, there may be also solid ice or ice ridges on the surface of the water 12.

The multi-purpose icebreaker 10 in FIG. 1 is provided with two azimuth propulsion devices 20 at the bow of the vessel. These azimuth propulsion devices 20 provide the only propulsion thrust for the vessel 10. For improving steering in difficult circumstances and for dynamic positioning the multi-purpose icebreaker 10 is also provided with three steering tunnel thrusters 21 at the stern of the vessel.

An advantage of the pulling mode azimuth propulsion devices 20 at the bow of the icebreaker 10 of FIG. 1 is that it is very easy to steer the icebreaker in the heavy ice conditions. The icebreaker 10 can easily make turns and it can be steered for widening the breadth of the required channel to be formed in the ice.

The propulsion devices 20 at the bow of the icebreaker 10 also give very good characteristics for the vessel when it is needed to move forward continuously at slow speed and ramming is not possible. The presented icebreaker 10 can push through the solid ice and ice ridges.

The second advantage of the propulsion devices 20 at the bow of the icebreaker 10 of FIG. 1 is that the propellers in front of the vessel crush the ice blocks smaller. Then the ice blocks do not disturb the other vessel to be towed or some other equipment close the vessel, as described below.

FIG. 2 presents the second embodiment of the multi-purpose icebreaker 10 according to the invention. The icebreaker 10 is also attached to another ship 11 for towing or other purpose. In FIG. 2 the icebreaker 10 is also provided with two azimuth propulsion devices 20 at the bow of the vessel. In this embodiment of the icebreaker 10 these azimuth propulsion devices 20 are not the only propulsion apparatuses of the vessel 10, but they provide the main propulsion thrust for the icebreaker 10.

The difference of the icebreaker 10 of FIG. 2 compared to the icebreaker 10 of FIG. 1 is that in FIG. 2 the icebreaker 10 is provided with two smaller azimuth thrusters 22 at the stern of the vessel 10. The azimuth thrusters 22 are mainly intended for improving steering in difficult circumstances and for dynamic positioning. However, they can also be used for forward thrust together with the main azimuth propulsion devices 20 at the bow of the vessel, so increasing the total forward thrust of the icebreaker 10.

In FIG. 3 there is described the third embodiment of the multi-purpose icebreaker 10 according to the invention. This icebreaker 10 is provided with conventional shaft propellers 30 in front of the vessel. These shaft propellers 30 provide the main forward thrust for the vessel 10. In order to improve steering the multi-purpose icebreaker 10 is provided with three steering tunnel thrusters 21 at the bow of the vessel and with two smaller azimuth thrusters 22 at the stern of the vessel 10.

The small azimuth thrusters 22 at the stern of the vessel 10 are mainly intended for improving steering in difficult circumstances and for dynamic positioning. However, as described in FIG. 2, they can also be used for increasing forward thrust together with the conventional shaft propellers 30, which are the main propulsion devices of the icebreaker 10.

FIG. 4 presents the multi-purpose icebreaker 10 of FIG. 1 provided with a turret 40 for loading oil to the tanker vessel 11 attached to the icebreaker 10. In FIG. 4 the turret 40 is provided with oil tubes 41 and anchor wires 42. In this case the azimuth propulsion devices 20 at the bow of the icebreaker 10 are very useful because they keep the turret 40, oil tubes 41 and anchor wires 42 clear from ice. The propellers of the azimuth propulsion devices 20 also crush the large ice blocks smaller.

FIG. 5 presents a bottom view of a multi-purpose icebreaker 10 according to the invention. According to FIG. 1 the icebreaker 10 is provided with an inward curved towing notch 15, two azimuth propulsion devices 20 a and 20 b at the bow of the vessel, and three steering tunnel thrusters 21 at the stern of the vessel. In the bottom of the icebreaker 10 the turret 40 is located in the middle of the ice plough 16, so that the ice plough 16 forms a protecting shelter around the turret 40. In FIG. 5 it can be clearly seen the protective function of the ice plough 16. The azimuth propulsion devices 20 a and 20 b at the bow of the vessel 10 push the ice blocks along the sides of the ice plough 16, so preventing the ice blocks from striking the turret 40 or the equipment, such as the oil tubes 41 and anchoring wires 42 attached to the turret 40.

It is obvious to a person skilled in the art that the different embodiments of the invention may vary within the scope of the claims presented below.

REFERENCE NUMERALS

10 Multi-purpose icebreaker

11 Vessel

12 Water

15 Towing notch

16 Ice plough

20 Main azimuth propulsion device

21 Steering tunnel thruster

22 Smaller azimuth propulsion device

30 Conventional shaft propeller

40 Turret

41 Oil tube

42 Anchor wire 

1. Multi-purpose icebreaker (10) having a front part, an aft part, at least one main propulsion device (20, 30) and at least one steering device (21, 22), wherein the multi-purpose icebreaker (10) comprises at least one main propulsion device (20, 30) located in the front part and at least one steering device (21, 22) located in the aft part.
 2. Multi-purpose icebreaker (10) according to claim 1, wherein the multi-purpose icebreaker (10) has, in the front part, two main propulsion devices (20, 30), which are azimuth propulsion devices (20), and, in the aft part, the steering device (21, 22) comprises at least one tunnel thruster (21).
 3. Multi-purpose icebreaker (10) according to claim 1, wherein the at least one main propulsion device (20, 30) in the front part comprises two azimuth propulsion devices (20), and the steering device (21, 22) in the aft part comprises at least one azimuth propulsion device (22), which is smaller than the main propulsion devices in the front part.
 4. Multi-purpose icebreaker (10) according to claim 1, the at least one main propulsion device (20, 30) in the front part comprises two conventional shaft propulsion devices (30), and the at least one steering device (21, 22) in the aft part comprises at least one azimuth propulsion device (22).
 5. Multi-purpose icebreaker (10) according to claim 1, wherein the at least one main propulsion device (20, 30) in the front part comprises two conventional shaft propulsion devices (30), and the at least one steering device (21, 22) in the aft part comprises one or more tunnel thrusters (21). 